The present invention relates to a safety belt retractor such as a safety belt retractor intended for use within a motor vehicle. More particularly the invention is concerned with a safety belt retractor incorporating an arrangement to provide an indication as to whether or not the safety belt is being used by an occupant in a motor vehicle.
In some countries it is a legal requirement that, where fitted, a safety belt be worn by an occupant of a motor vehicle. It is known to provide a motor vehicle with means for providing an audible or visual alarm when an occupant in the vehicle does not wear a safety belt.
It is known, for example, to provide an electric switch within the buckle of a safety belt arrangement in a motor vehicle, the switch providing a signal which indicates whether or not a tongue connected to the safety belt has been latched within the buckle. Such an arrangement requires the provision of an additional electrical connection to the buckle of the safety belt arrangement. It would be preferable if such a switch could be provided within the main body of the safety belt retractor where there may already be an electrical connection to a sensor or other component which is electrically powered.
It has also been proposed previously to provide a switch which is controlled by means of a pivoted arm which is spring biased into engagement with the webbing of a safety belt wound upon the spool of a retractor. The angular position of the arm provides an indication of the amount of webbing wound on the spool and thus the switch may provide a signal to indicate that the safety belt is not being used when the angular position of the arm indicates that all of the Webbing is wound on the spool.
This arrangement suffers, however, from the disadvantage that it causes a not insignificant amount of frictional resistance against rotation of the spool thereby necessitating the use of a stronger spring to wind the safety belt webbing onto the spool. The use of a stronger spring in turn makes the safety belt more uncomfortable to wear because it will impart greater tension to the belt so that the belt will feel particularly tight when being worn by an occupant in the vehicle. In addition the pivoted arm can cause a considerable amount of wear of the webbing which may, in the long term, result in weakening of the webbing.
Furthermore, in some retractor designs a relatively long spool or spindle is used, the length of which is greater than the width of the safety belt webbing. With such a spool the webbing may be spread over the length of the spool when it is fully wound thereon or, alternatively, the webbing may be wound on top of itself so that it is "concentrated" in one section of the spool. It will therefore be appreciated that with a spool of this type the diameter of the webbing wound upon the spool may not give a true reflection of the amount of webbing actually present on the spool.
The use of an arrangement for indicating when a safety belt is being used such as described above, in combination with a sensor located in a vehicle seat to provide an indication of the presence of an occupant upon the seat enables a signal to be obtained which indicates when an occupant of a vehicle seat is not using the safety belt provided for use with that seat. This signal may then be used to activate an alarm or to control the performance of a safety device such as an air bag.
The present invention seeks to provide an improved safety belt retractor having an arrangement to indicate when the safety belt is being used by an occupant in a motor vehicle.